Titanium trichloride is a well known component of Ziegler-Natta catalyst systems. The titanium trichloride employed in such systems is commercially available and most commonly produced by the reduction of titanium tetrachloride with aluminum metal. While catalysts employing titanium trichloride produced in this manner are extremely active, such catalysts have been found to promote the production of blocky resins having undesirably elevated levels of extractables and volatile oils when employed in the copolymerization of ethylene with higher alpha-olefins such as hexane. The cause of this high level of extractables and volatile oils is believed by the inventors herein to be attributable, at least in part, to the presence in such catalysts of a mixed crystal, TiCl.sub.3.1/3AlCl.sub.3, which is known to be produced when titanium tetrachloride is reduced with aluminum metal.
Titanium trichloride suitable for use in Ziegler-Natta catalyst systems can also be prepared by the reduction of titanium tetrachloride with hydrogen gas. However, this method is extremely costly and results in the production of an environmentally undesirable by-product, i.e., hydrogen chloride.
Still another method of producing titanium trichloride is by reducing titanium tetrachloride with an organomagnesium compound such as a dialkylmagnesium compound or an alkyl magnesium halide. However, this method also is extremely costly and, like the hydrogen reduction method, results in the formation of undesirable reaction by-products, in this case chlorinated alkanes, which must be separated from the desired titanium trichloride product before it can be used.